Spark plug hole construction and method

ABSTRACT

The spark plug hole of an engine part is provided with a bushing including an internally threaded collar united in a gas tight manner, only at its inner end, to the engine part and the outer end providing upon a radial flange a seat for the spark plug. The method of engine part construction includes reboring the original spark plug hole so that the bushing may be mounted therein, welding only the interior disposed end of the bushing and correcting any distortion of the internal threads in the bushing.

United States Patent Tarter [451 Aug. '15, 1972 [54] SPARK PLUG HOLE CONSTRUCTION 3,35 l ,043 l 1/1967 Morrison ,.29/402 3 AND METHOD 3.449.816 6/1969 Swick 123/32 [72 I ntor: Carl M. Tarter, Healdsburg, Calif. OTHER PUBLICATIONS I [73] Assignee: T&W Manufacturing Corp., Santa Rosa, Calif. Machine Design Fasteners Book issue, 1963, [22] Filed June 8 1970 Penton Publishing pages 103-107, 165-181 211 App] 44,1 2 Primary Examiner-Laurence M. Goodridge' Assistant Examiner-Ronald B. Cox 1 r Fl h H h, b 52 us. 01 ..123/4l.82,- 123/32 R, 29/401, A'tiomey e hbac Herbert 29/427, 29/479, 123/169 R 57 ABSTRACT [51] Int. Cl. ..F02t1/36, F22d 19/10 1 a [58] Field of Search 123/32, 41.82; 29/401, 402, The p r Pl l of nq sm P 18 p q wlth 29 427 479 a bushmg mcludmg' an internally threaded collar united in a gas tight manner, only at its inner end, to 5 References Cited the engine part and the outer end providing upon a radial flange a seat for the spark plug. The method of UNITED STATES PATENTS engine part construction includes reboring the original spark plug hole so that the bushing may be mounted 3 gl fggifi therein, welding only the interior disposed end of the 1 42 8/1954 {/4795 bushing and correcting any distortion of the internal y v v u e n n n I a u I e a I a u n o u a a a I 3,187,729 6/1965 MOITISOl'l ..l23/32 4Claims,6Dr awingFiures P'A'TENTEnnums m2 3,683,873

INVENTOR.

Carl M. Tartar ly/Mn, Wfhli SPARK PLUG HOLE CONSTRUCTION AND METHOD BACKGROUND OF THE INVENTION With engines made from non-ferrous metals, it is not uncommon that the threads for the spark plug hole become damaged or stripped causing leakage and improper sealing of the spark plug. Furthermore, cracks frequently develop between the valve seats and spark plug holes during the life of an engine and it is'desirable that these conditions be remedied during engine over haul.

Conventional practice included inserting heli-coils into the spark plug holes to supplement the damaged threads therein. It was found that this arrangement is unsatisfactory because the heli-coils within the spark plug holes did not insure a gas-tight seal, and frequently the engines pressures would cause the heli-coils" and spark plug to loosen. Another expedient for repairing a damaged spark plug hole was to rebore and retap the hole for the next larger spark plug size. However, the removal of metal and substitution of the next larger plug size weakened the engine part structure and increased susceptibility to cracking between the valve seats and spark plug hole.

SUMMARY OF THE INVENTION AND OBJECTS In summary, the invention pertains to a spark plug hole construction involving an engine part having a surface which forms at least part of a combustion chamber, there being a hole therein opening through the surface. A bushing having internal threads for receiving a spark plug is mounted through the hole with one end of the bushing terminating adjacent to the surface of the combustion chamber. The bushing and the engine part are formed of materials which have suba relatively smooth bore, positioning the above bushing in the rebored spark plug hole and welding the end of the bushing to the engine part so that the bushing is substantially flush with the surface of the combustion chamber and forms a gas-tight seal therewith.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view through an engine part taken at a plane extending vertically through the spark plug and hole therefore and illustrating the present invention.

FIG. 2 is a view like FIG. 1 of the engine part in the original state.

FIG. 3 is a horizontal sectional view looking from below of the engine part of FIG. 1 at one stage of remanufacture.

FIG. 4 is a view like FIG. 1 showing another stage of engine part remanufacture.

FIG. 5 is a view like FIG. 3 showing still a further stage in engine part remanufacture. 1

FIG..6 is an enlarged sectional view of a bushing em ployed in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the accompanying drawing there is shown an internal combustion engine part 11 which may be either a cylinder block 'or head and more particularly of the type used in air-cooled engines wherein flns or registers 12 dissipate the engine heat to the: atmospheresThe engine part 11 may be of any suitable metal such as an aluminum alloy of the type commonly used in such internal combustion engine parts. For the purposes of this invention, the engine part 11 is the part which carries the spark plug or plugs in an internal combustion engine. Such an internal combustion engine can be of any type which uses spark plugs such as a stationary, automotive, or motorcycle engine. The engine part 11 which is shown in the drawing isthe head of an aircooled internal combustion automotive engine of the type manufactured by Volkswagon. The head is removably secured to the associated engine block (not shown). A cylinder liner 14 is mounted in the engine block for each of the cylinders (not shown) in the engine block. Intake and exhaust valves 16 and 17 are mounted in the head 11 for each cylinder of the engine. The valves 16 and 17 cooperate with valve seat inserts 19 mounted in the head 11. The valve seat inserts are constructed in the manner disclosed in US. Pat. No. 3,487,823-1ntermediate the poppet valves 16 and 17 a spark plug 19 is positioned. Referring to FIG. 2, there is shown the cylinder head 11 having therein the original spark plug hole 21 which during the service life of the engine may have become cross threaded or the combustion chamber may have developed cracks 22 (FIG. 2) extending from the spark plug [hole and propagating towards the valves. FIG. 1 shows a bushing 24 mounted in the cylinder head, the bushing including an internally threaded collar 26 having a radially extending flange 27. The threads of the collar 26 are complimentary to the standard threads of the spark plug 19 while the axial length of the bushing 24 is equivalent to the reach of the spark plug intended for the engine. To this end, the radial flange 27 provides a surface upon which the spark plug 19 seats.

The bushing 24 is preferably formed of material having generally the same coefficient of expansion as the cylinder. head. The bushing, for example, may be formed of 201 l-T3 aluminum while the cylinder head may be formed of an aluminum base alloy of the type commonly used in 'such internal combustion engine parts. As shown in FIGS. 1 and 6, the bushing 24 is rigidly secured as by welding to the block or head 11 at only the inner end thereof which is beveled at 28 to accommodate the welded metal to insure the forming of a gas-tight seal between the engine part and bushing 24. Preferably, the outside diameter of the collar of the bushing is formed from 0.001 to 0.003 inches oversize with respect to the associated hole 31 so as to form an interference fit between the bushing and the cylinder head. To provide a seat for the radial flange 27, the cylinder head is counterbored as at 32 so that the bushing and the spark plug it will accommodate can project the proper distance with respect to the combustion chamber.

The method of reconditioning engines in accordance with this invention is as follows:

The original spark plug hole 21 is rebored as shown in FIG. 3 to accommodate the bushing 24 thus removing the original spark plug threads from the hole. At the time of the boring of the new hole 31, the counterbore 32 may be formed on the outside of the cylinder head. The bushing 24 is provided as shown in FIG. 6 and should have an outside diameter in the collar portion on the order of from 0.001 to 0.003 inches larger than the hole 31. The bushing 24 is inserted in the hole by force so as to achieve the press fit. The radial flange 27 seats securely within the counterbored portion 32, as shown in FIG. 4. As a next step, weld metal 29 is deposited in the Vee formed by the bevel 28 and the walls of the hole in the cylinder head. In this operation, any cracks 22 extending between the hole 31 towards the valves may be welded thus reinforcing the combustion chamber. As a follow-up operation, the internal threads of the collar may have become deformed and a tap may be run through the bushing so as to chase or clean up the threads and relieve whatever distortion may have been induced therein by either the welding or the press fitting operation.

It will be recognized from the above that the bushing is fixed only at one end to the cylinder head. Thus, as the engine temperature rises during engine operation, the metal bushing will expand axially only in an outward direction and not further into the combustion chamber. The advantage is that the spark plug electrode position does not change appreciably during engine operation albeit the plug is mounted in a bushing member.

The machine operations for overhauling the spark plug hole may be performed with conventional machine tools including the welding operation which may be performed by the inert gas shielded arc process.

The representations in the text and drawings have been intended merely to facilitate the practice of this invention by persons skilled in the art and no unnecessary limitations are intended thereby, for the scope of the invention is delimited in the following claims.

I claim:

1. In a method for constructing a spark plug hole in an engine part having a surface which forms at least part of a combustionchamber and having a defective threaded spark plug hole therein extending through the said surface by utilizing a bushing having internal threads serving to accommodate a spark plug, reboring the defective spark plug hole of the engine part from 0.001 to 0.003 inches undersize with respect to the bushing so as to remove the original threads and to proa radial flange at one end, together with the step of counterbormg the engine part at the exterior around the spark plug hole to a diameter at least as large as the radial flange of the bushing and to a depth at least as great as the thickness of the flange.

3. In a spark plug hole construction, an engine part having a surface which forms at least part of a combustion chamber, said engine part having a hole therein extending through the engine part and opening through said surface, a bushing mounted in said hole, said bushing having internal threads serving to receive a spark plug, one end of said bushing terminating adjacent said surface, said bushing and said engine part being formed of materials which have substantially the same coefficients of expansion, said bushing having a generally smooth exterior side wall continuous throughout its circumference and having an outside diameter which is on the order of 0.001 to 0.003 inches greater than the inside diameter of said hole, and being mounted with a pressed fit in said hole so that said bushing frictionally engages the side walls of the engine part forming the hole, a weldment securing said end of the said bushing to said engine part so that a gas-tight seal is formed between said bushing and said engine part, the remainder of said bushing being capable of expanding axially when the engine part becomes hot. 

1. In a method for constructing a spark plug hole in an engine part having a surface which forms at least part of a combustion chamber and having a defective threaded spark plug hole therein extending through the said surface by utilizing a bushing having internal threads serving to accommodate a spark plug, reboring the defective spark plug hole of the engine part from 0.001 to 0.003 inches undersize with respect to the bushing so as to remove the original threads and to provide a relatively smooth bore, press fitting the bushing into the rebored spark plug hole so that one end of the bushing is substantially flush with the surface forming the combustion chamber, and welding said end of the bushing to the engine part so that the bushing is substantially flush with said surface and forms a gas-tight seal with the engine part, the remainder of the bushing being free to expand in an axial direction in the engine part at engine operating temperature.
 2. The method as in claim 1 wherein said bushing has a radial flange at one end, together with the step of counterboring the engine part at the exterior around the spark plug hole to a diameter at least as large as the radial flange of the bushing and to a depth at least as great as the thickness of the flange.
 3. In a spark plug hole construction, an engine part having a surface which forms at least part of a combustion chamber, said engine part having a hole therein extending through the engine part and opening through said surface, a bushing mounted in said hole, said bushing having internal threads serving to receive a spark plug, one end of said bushing terminating adjacent said surface, said bushing and said engine part being formed of materials which have substantially the same coefficients of expansion, said bushing having a generally smooth exterior side wall continuous throughout its circumference and having an outside diameter which is on the order of 0.001 to 0.003 inches greater than the inside diameter of said hole, and being mounted with a pressed fit in said hole so that said bushing frictionally engageS the side walls of the engine part forming the hole, a weldment securing said end of the said bushing to said engine part so that a gas-tight seal is formed between said bushing and said engine part, the remainder of said bushing being capable of expanding axially when the engine part becomes hot.
 4. A construction as in Claim 3 wherein said bushing is provided with a flange on its outer end and said engine part is provided with a counterbore which receives said flange. 